Bokeh or defocus in Blender's default render engine?
If you select your camera, and go to the camera tab on the properties bar, there should be a Depth of Field tab.


You can change the object that will be the focus point, or you can input a distance instead. Change the value of F-Stops to achieve the Depth of Field/Blur effect you're going for.
As for Bokeh, tick the High-Quality box and you can change the number of blades to whatever bokeh effect you're trying to achieve.